Zeolites are microporous crystalline structures that are widely applied as catalysts in the petroleum and chemical industries. Transport of molecules through zeolitic micropores occurs by diffusion and is believed to affect the rate of a reaction. However, the microporous network limits diffusion, hindering access to the active sites and limiting the reaction rate. Attempts have been made to improve catalytic effectiveness by the introduction of mesoporosity into the micropore structure. Mesopores provide improved access to the micropores thereby enhancing the rate of diffusion and thus the catalytic performance.
An effective method of increasing mesoporosity in zeolites has proven to be the selective extraction of silicon from a zeolite framework, referred to in the art as desilication. The use of desilication to increase the mesoporosity of mordenite, is for example, described in WO 2008/147190. In WO 2008/147190, a mesoporous mordenite is prepared by subjecting a non-dealuminated mordenite having an atomic ratio of framework Si to Al of at least 15, to an alkaline treatment, such as sodium hydroxide, in order to create mesoporosity by removal of silicon.
U.S. Pat. No. 5,118,482 describes a process for realuminating zeolites, thereby reducing their silica alumina ratio whereby the framework aluminium content of a framework deficient zeolite containing non-framework aluminium is increased by contacting the zeolite with an aqueous basic solution at a temperature greater than about 25° C.
Zeolites, such as mordenite are known to catalyse hydrocarbon conversion reactions, such as hydrocracking and the transalkylation of hydrocarbons. For example, U.S. Pat. No. 3,619,412 describes the preparation of a hydrocracking catalyst by impregnating a support consisting of a mixture of mordenite and amorphous silica-alumina with a solution of a fluorine compound, drying and treating with a solution containing one or more hydrogenative metals. U.S. Pat. No. 4,039,479 describes a method of manufacturing a catalytic composite by subjecting a mordenite with a sodium content of less than 5 wt % as Na2O to an aqueous ammoniacal treatment at a pH of at least about 9.5, calcining in intimate admixture with a non-zeolitic refractory inorganic oxide, such as alumina and a metal salt convertible to said oxide at calcination conditions, such as aluminium salts. It is stated that the inclusion of the metal salt in admixture with the zeolite and refractory inorganic oxide has been found to effect a significant improvement in the activity of the catalytic composite produced therefrom, particularly with respect to the transalkylation of alkylaromatic hydrocarbons.
Carbonylation processes for the production of acetic acid and/or methyl acetate by carbonylating methanol and/or reactive derivatives thereof with carbon monoxide are known. Such processes typically employ Group VIII metal catalysts, such as rhodium and iridium. Mordenites are also known to catalyse carbonylation reactions. For example, there is described in EP-A-1 985 362 a process for the carbonylation of dimethyl ether in the presence of a mordenite catalyst. In EP-A-1 985 362 it was found that improved catalytic activity could be achieved by using a mordenite catalyst which had been loaded with silver and/or copper and also a low level of platinum.